Same issue as everyone else, wish I would've looked a little sooner. I've got a March 2012 model and this started just after warranty with a shadow that my kids got blamed for, Don't Touch Dads Laptop, feeling bad about that now.
It slowly moved across my screen until it wasn't worth using the built in display. *** when you buy a laptop and it turns into a really expensive desktop.
The only upside is that i use a 50" screen
If Dell could get passed the 7/10 rule of only 7 out of 10 products have to work correctly to meet expectations and goals just maybe they would have better ratings.
Their honestly lucky theirs so many people in this wonderful world to sucker in.